Echo repeater



E. M. M MILLAN EI'AL 2,694,868

ECHO REPEATER 4 Sheets-Sheet l Nov. 23, 1954 Filed Aug. 5, 1943 INVENTORS EDWIN MMMILLM AND WILLIAM A.MYEIZS BY ATTORNEY NOV. 23, 1954 M, McM N E 2,694,868

ECHO REPEATER Filed Aug. 3, 1943 4 Sheets-Sheet 2 FIGA.

INVENTORS EDWIN M. wmummo mum A.MYER S BY ATTORNEY Nova 1954 E. M. MGMILLAN ETA].

ECHO REPEATER 4 Sheets-Sheet 3 Filed Aug. 3, 1943 EOE ow 5.5m 12a INVENTORS EDWIN M MMILLAN AND WILLIAM A, MYERS ATTCR \EY N 1954 E. M. MCMILLAN EI'AL 3,

ECHO REPEATER Filed Aug. s, 1945 4 Sheets-Sheet 4 INVENTORS EDWIN MMMILLAN AND WILLIAM A. MYERS BY ATTORNEY United States Patent ECHO REPEATER Edwin M. McMillan, San Marino, and William A. Myers, San Diego, Calif., assignors to the United States of America as represented by the Secretary of the Navy Application August 3, 1943, Serial No. 497,232

3 Claims. (Cl. 3510.4)

This invention relates to a target device for receiving and amplifying sound.

Of recent years in several allied fields there has come the need for a device for receiving sound signals, after such signals have traveled a relatively great distance, in order that they might be amplified and retransmitted for another relatively great distance. This need has developed from problems met in both water and air transmission where signalling and repeating operations are often carried on.

A particular application of such a device for which important use has recently been found is one which will receive underwater sounds, amplify them and re-transmit them to their point of origin, Without regard for their directional aspects. One of the objects of our invention is such a device, very useful in measuring distances between ships, submarines, buoys, bottom, submerged objects, etc.

For instance, if a ship were fitted with such a device, and a sound signal were transmitted in its direction, the signal could be received, amplified and again transmitted back to its point of origin. By means of proper receiving and timing mechanisms'located at that point of origin the operator would be advised as to both the direction and distance of the ship on which the gear was mounted. It is thus a further object of our invention to provide such a device for determining direction and distance.

A further important application is one arising from the lack of equipment in training operators in the use of sound or echo-ranging gear. In time of war the need for submarine protection and detection increases as the equipment available for training personnel in the use of gear for such purposes correspondingly decreases. This training primarily consists in teaching the operation of echo-ranging equipment designed to project a sound signal and to receive the echo of that signal if it is reflected from a target such as a submarine. A well trained operator is exceedingly valuable because his training is extensive and involves considerable actual practice. His training also involves the use of costly equipment which is often not procurable. In other words, until now it has been necessary to position a ship or submarine as a target so that actual practice in echo ranging could be had. This invention has for another purpose the elimination of this equipment and substitutes for it a receiver and amplifier for. reproducing a simulated echo for retransmission to the originating point.

A still further object of this invention is an echo repeater of the character described which operates relatively free of acoustic or electrical coupling.

Still another object of this invention is an echo repeater which is mobile and thus further simulates a characteristic moving target.

Yet another object of this invention is an echo repeater which may be towed under water at a given depth, so that the echo ranging ship may pass over the device during the course of movement.

Still another object of the invention is an echo repeater which will repeat the sound signal without an appreciable time delay, which delay would introduce error into the range or distance measurements.

An even further object of the invention is an echo repeater of the character described which can be electrically controlled while moving under water.

An additional object of the invention is an echo repeater which is non-directional and may be used as a target by many ships simultaneously.

And another object of our invention is an underwater signalling device.

From what has already been said it is obvious that the invention, in its most useful form, is one which might be termed an echo repeater; and its primary use is for training sound operators. It is likewise obvious that the device might be built in several different forms, all of which operate on the same principle. In any case, two transducers, a hydrophone and a projector, are mounted on a frame or float which is suspended or towed in the water. The transducers are connected to the input and output of an amplifier, designed to pass the desired frequencies which, in the case of simulated echo ranging, would be those used in such operations. The mounting must be such that the acoustic coupling between the two transducers is as small as possible, by taking advantage of the minima in the directivity patterns, and/or by the use of bafiies and insulators.

In operation, a signal picked up by the hydrophone is re-transmitted from the projector with increased intensity. The amount of increase and the strength of the echo produced depend upon the gain of the amplifier. Naturally the maximum gain that can be obtained is determined by the occurrence of feedback oscillation caused by the residual acoustic coupling between the transducers when the gain is too high. It is this problem which causes the greatest difficulty and is overcome by the invention described herein.

From the preliminary statement of objects it is obvious that the general disclosure can be utilized in several applications. It has been found that with obvious dilferences, the echo repeater may be mounted on a buoy either at or below the surface at a predetermined distance. It may also be mounted on a small boat, which enables the simulation of a moving surface target, or, for the same purpose, on a raft capable of being towed. However, the most important application, and the one which finds most extensive use, is one which is capable of being towed under water at any predetermined depth. This last application has for its primary advantage the fact that it simulates most closely the action of a submarine target, because it may not only be towed under water but also because, if the tow line is sufficiently long, practicing ships may pass directly over it, as would be the case with a submarine.

The general electrical principles involved in all of the applications are the same. However, for purposes of this application, the underwater towed model will be illustrated and described in detail. It is to be clearly understood that the model described is only illustrative and that in addition to the mechanical mounting shown, the other above-mentioned models are only modifications of such general principles.

In the drawings which illustrate the invention as embodied in the model adapted to be towed under water:

Fig. l is a side elevation with part of the head and body cut away showing the ballast and amplifier;

Fig. 2 is an end elevation of the device shown in Fig. l, the fins being only partially shown;

Fig. 3 is a detailed sectional view of the mechanism for attaching the cable to the head;

Fig. 4 is an enlarged, vertical sectional view through one of the transducers on the assembly view shown in Fig. 1;

Fig. 5 is a sectional view taken on lines 55 of Fig. 4;

Fig. 6 is a plan view of the transducer shown in Fig. 4;

Fig. 7 is a schematic wiring diagram of the amplifier and control circuits; and

Figs. 8 and 9 are directivity patterns of the transducers.

Referring now to the drawings, the underwater towed model is mounted in a metal container, generally designated 1. The main section is a hollow metal cylinder 2 which is tapered, as at 3, at its rearward end. The tapered end 3 is closed by an end plate 4. The forward end is formed with a series of studs 5 around its circumference. A head, generally designated 6, fits on this forward end as shown in Figure 1. The head is formed with a centrally positioned extension 7 containing set screws 8 for a purpose to be described later.

Around and near the circumference of the head 6, is a series of tubular members 9 positioned to receive the studs 5 when the head is placed in position. Nuts are provided on the studs to bolt the head onto the cylinder.

Located at the rearward end of the cylinder 2, and extending almost to the end of the tapered portion 3, are four fins. Two of them 11, 12 are welded above and below the cylinder in a vertical plane as shown in Figure 1. The lower fin 12 is formed with a generally rectangular notch 13 extending upwardly from its lower edge to a point near the connection of the fin to the cylinder. At the upper edge of the notch a circular ring 14, formed with depending circular flange 15, is welded into place in a position perpendicular to the plane of the fin. A Corprene insulator 16 is fitted within flange 15. While the insulator has been specified to be of Corprene, a commercial product composed of cork and neoprene, any other suitable material may be used. This insulator also has a peripheral flange 17 which is designed to extend around one end of a cylindrical transducer 18. The transducer occupies the notch 13 and is also held in place by a similar Corprene insulator 19 with a flange 26, which insulator is adapted to fit over its opposite end. The whole unit is secured by means of a circular cover plate 21 which is formed with an upstanding flange 22 to receive the insulator 19. A heavy metal ring 23 is welded into place at the lower end of the notch and the cover plate is bolted to this ring by means of bolts 24. Thus, when the transducer is in place it can be secured in position by tightly screwing the cover plate 21 to the ring 23. At the upper end of the transducer 18 is a conventional waterproof coupling 25 which extends through ring 14 and insulator 16. A similar coupling 26 is mounted in the tapered portion 3 of the cylinder 2, adjacent coupling 25, so that an insulated conductor sheath 27 may extend from the transducer to the amplifier assembly mounted inside the cylinder. At the lower end of fin 11 are four ballast blocks 28 to maintain the repeater on an even keel, only two of them being shown.

The upper fin 11 is fabricated identically with fin 12 and carries another transducer 29 mounted in the same manner as transducer 18. However, no ballast blocks are included on its upper edge.

Two horizontal fins 30, 31 (see Figure 2) are mounted in position similar to vertical fins 11 and 12. These horizontal fins are of the same shape as the vertical fins but carry no transducers or ballast blocks.

At the forward upper end of the cylinder 2 a lifting ring 32 is welded in place to receive the end of cable if it is desired to lift the whole assembly.

Where it has not been specifically mentioned, all parts are welded for greater strength.

The central extention 7 of the head 6 is shown in Figure 3. It carries a connector 33 which is centrally drilled to receive the tow cable 34 and is held in place by the screws 8. The central hole is enlarged as at 35 near the rearward end. A centrally drilled guide 36, with a flange 37 at one of its ends, is positioned within this enlarged portion; and a ring 38 is bolted over the end of the connector by means of bolts to hold the guide in place. The flange 37 is drilled with a plurality of small holes each one of which is designed to receive one of the strands of the multi-strand tow cable 34. Each strand is then turned about the shank of the guide 36 and molten lead is poured over it to make a strong solid joint. The tow cable 34 carries insulated conductors 39 positioned along its center. The insulated conductors 39 are shown in Figures 1 to 3 as a co-axial cable having two conducting wires surrounded by insulation. These conductors are shown schematically in the wiring diagram, Figure 7. These conductors are brought through the centrol holes in guide 36 and ring 38 for connection to the amplifier. A conventional waterproof coupling 40 is positioned at the rearward end of extension 7 through which the electric conductors extend.

A pressure-depth gauge 41 is also mounted inside the head 6. This may be of any conventional type for providing a contact in an electrical circuit. The one shown is of the diaphragm type mounted on a small bracket 42 inside the head. A short tube 43 extends through the head to allow the water pressure to be exerted on the diaphragm.

The whole unit is balanced by introducing lead ballast 44 into the bottom of the cylinder 2, as shown in Figure 1. This ballast should be of a weight to give the whole assembly a slight positive buoyancy. The amplifier assembly, to be described is mounted on the lead ballast as shown in the cut out part of Figure 1.

The electric circuit designed for use with the echo repeater is not complex. In addition to the related power supply the unit consists of a four stage amplifier, a hydrophone, a projector, and two indicating devices, one for indicating depth, the other for indicating behavior of the amplifier.

The power supply which has been found satisfactory is a 12-volt or two 6-volt storage batteries. The battery may be mounted within the main cylinder 3, but because the acid is likely to spill we have found it more satisfactory to place the battery in the towing boat and carry the power down the cable to the amplifier, as shown in Figure 7. Power from the battery is supplied at terminals A, which are connected to the center poles or a double-pole double-throw switch 45. The lower poles (as in Figure 7) of the switch connect to an inverter 46 which converts the D. C. voltage to A. C. (about 132 volts in this case). After passing through a fuse, this voltage is supplied to terminals B, one of which is grounded as shown. The ground terminals are indicated by either opened or closed symbols in the drawings. The opened symbols represent the potential of the chassis ground while the closed terminals represent B or the signal ground.

The portion of the circuit just described, together with the indicating devices, is mounted, in this illustrative case, in the tow boat. The terminals B are connected to terminals C on the amplifier (mounted in the echo repeater) by means of a long piece of special insulated cable 34. This cable is preferably comprised of a plurality of strands of strong wire wound about its outer surface, with electrical conductors 39 insulated and sealed into its central portion. These electrical conductors are indicated in Figure 7 in dotted lines.

it has been found that this type of cable has considerable ohmic resistance which may cause a voltage drop between the terminals. Thus, in practice, a voltage of about 120 volts is delivered to the amplifier circuit in the normal way through the power transformer 47, the rectifier 48 and the filter system 49;

Terminals D and E on the amplifier chassis are connected to the hydrophone 18 and the projector 29 respectively, through their corresponding leads. Signal voltages generated by the hydrophone are impressed upon the grid of the first tube 50 of the amplifier, through the impedance matching transformer 51. The suppresser grid is tied to the cathode of tube 50 and the two are grounded through resistor 52 and capacitor 53, while the grid is by-passed to ground through capacitor 54. Resistors 55, 56 and 57, in conjunction with resistor 52, form a voltage divider system for supplying the proper screen grid, cathode, and plate voltages. Capacitor 53 serves to bypass any A. C. voltage present at this point to ground.

The amplified signal voltages are, after passing through filter system 59, impressed upon the grid of tube 69. Capacitor 61 serves as a by-pass for the cathode and suppresser grids; and resistor 62 limits the value of gain provided by the gain control 63. Inductors 64, 67 are the plate load inductors and resistors 65, 66, and capacitor 68 perform the same functions as do resistors 55,, 5,6, and 57 and capacitor 58, in connection with tube 5.0. Capacitor 69 provides a screen grid by-pass for tube .60. The plate of tube 60 is capacity coupled, by means of capacitor 70, to the two paralleled grids of tube 71, which acts as a driver for the power tube. Resistors 72, 73 serve as grid and cathode resistors, respectively, While capacitor 74 by-passes the cathode of tube 71 to ground.

The plates of tube 71 are connected in parallel through inter-stage transformer 75 to the push-pull grids of the output stage. Resistor 76 is the plate dropping resistor or" tube 71 and capacitor 77 serves as a by-pass for this circuit. The output stage comprises a twin triode 78,

,1 operating at zero bias in class B. A class B amplifier is an amplifier in which the grid bias is approximately equal to the cutoflf valve, so that the .plate current is approximately zero when no exciting grid voltage is applied, and so that plate current in a specific tube flows for approximately one-half of each cycle when an alternating grid voltage is applied.

Resistor 79 is the secondary load resistor of transformer 75. Capacitor 80 is a plate loading capacitor for the output transformer and the power from this output stage is delivered through impedance matching transformer 81 to terminals E (which connect to projector 29).

Also coupled to the output coil of transformer 81 is the grid of a signal amplifier tube 82, through resistor 83. Resistors 84, 85 serve as its cathode and grid resistors respectively, and capacitor 86 is the cathode by-pass. Capacitor 87 serves a purpose analogous to capacitor 80 and the plate of tube 82 is coupled through transformer 88 and capacitor 89 to the insulated conductor 39 of the tow cable.

The device, as has been stated, is provided with a pressure-depth gauge 41 which is connected into the circuit at terminal F. This gauge is connected to a visible surface indicator 90 through a double-pole double-throw relay 91 and the conductor 39. In conjunction with switch 45, the depth gauge indicator circuit may be manually controlled. Thus, if switch 45 is thrown to its upper position (in Figure 7), no A. C. voltage is furnished to the system, but the D. C. voltage, at terminals A, is supplied to the indicator 90, and to the depth gauge 41 (through terminal F). This follows necessarily since while no A. C. voltage is supplied relay 91 is in its normal position. However, if switch 45 is manually thrown to its lower position, D. C. voltage is supplied to the inverter 46 and the coil of relay 91 (through the control cable 39). This actuates relay 91 so that its terminals are closed to the left to connect the manual surface gain control 92 through conductor 39 and filter system 93, to the grid of tube 50 of the amplifier.

In order that the operator may observe the behavior of the amplifier at the surface of the medium in which the device 1 is towed, as for example in the boat towing the device, a small portion of the output of the amplifier is impressed upon the cable 39 and is observed by indicating milliammeter 94. The frequency at which the amplifier operates is very much higher than the supply voltage and is separated and filtered by means of a resonant filter composed of capacitor 95 and inductor 96. An instrument rectifier 97 is provided to convert the high frequency A. C. signal for use on the D. C. indicating meter 94. Resistor 98, together with capacitor 95, is provided to isolate the indicating circuit from the A. C. supply. Meter 94 is also shunted by a variable resistor 99. Pilot light 100, protected by resistor 101, and voltmeter 102, are connected across the output terminals of the inverter 46.

In order that the D. C. operated depth gauge 90 may be used on the two conductor co-axial cable 39, supplying A. C. to transformer 47, it is necessary that the D. C. be effectively blocked from the winding of the transformer. This is accomplished by means of two pairs of capacitors 103, 104 placed at the ends of the cable. The pairs of capacitors are of the electrolytic variety and must be provided with polarizing potential. On the surface, battery 105 and resistor 106 provide this voltage, and on the amplifier end of the line this same function is performed by means of the voltage dividing resistors 107, 108. It is of course obvious that capacitors other than the electrolytic type may be used.

Of course, other amplifier circuits could be used with good results. The one described herein has proven very satisfactory and meets the requirements that it pass only the desired frequencies, which in the case of echo-ranging, may be in the supersonic range, and be portable, through battery operation.

The transducers consisting of the hydrophone 18 and the projector 29 are alike in structure and therefore only one, the hydrophone 18, has been shown. Referring now to Figs. 4, and 6, a cylindrical rubber casing 109 having end caps 110 and 111 and an inner, perforated metallic sleeve 112 is provided for supporting therein a stack of Rochelle salts X-cut crystals 113. These crystals are separated from each other by Corprene spacers 114 and are connected in parallel by means of the conductors 115 116 and terminal strips 117, 118. To secure the crystals in stacked relation, Corprene strips 119, 120 may be utilized and these together with the stacked crystals 113 are held in place by upper and lower Corprene discs 121 and 122 respectively.

The conductors 115 and 116 extend upwardly through apertures in the disc 121, thence through drilled screws 123, 124 secured in rubber grommets 125, 126 and through sheath 27 into the hull 3 as shown in Fig. 1.

Operation It was mentioned hereinbefore that prior to our invention, all systems with which the applicant is acquainted of training personnel in the use of echo ranging equipr'nent for underwater detection of submarines required the use of an actual submarine. Smaller objects could not be towed beneath the surface to simulate a submarine because the surface presented by the smaller object was not large enough to effect an adequate reflection of a supersonic sound wave. However, in our novel device which has been described, the signal is received, amplified and then re-transmitted to the sending station with an adequate intensity. It therefore simulates very closely the actual echo which would be received from an actual submarine.

In operation the echo repeater is lowered into the water by means of cables attached to ring 32. These cables are then released and the tow line 34 is payed out. It is found that the depth at which the unit will tow is dependent upon the speed of the tow boat and the length of tow cable used, and for any given speed and length of tow line, it will remain at a given depth. The desirable depth is determined by operating conditions and during the early part of the run, switch 45 is thrown to its upper position to supply power to the depth indicator 90. Since no A. C. power is being supplied to the amplifier under these conditions, relay 91 is in its normal position so that the pressure gauge unit 41, in the nose of the repeater, is connected to the surface indicator to indicate the depth at which the relatively small echo repeater is being towed in simulation of an actual submarine.

When the proper depth and static towing conditions are reached, switch 45 is thrown to its other position. This disconnects the depth gauge and indicator and supplies power to the inverter 46, which in turn supplies A. C. to the amplifier through the conductor 39 and the relay 91. When a sound signal is received by the hydrophone 18 it is fed to the amplifier and, after amplification, introduced into the water by projector 29.

At this point in the explanation of the operation, reference should again be made to the gain of the system. One of the most difiicult problems in connection with the invention is maintaining sufficient gain, without acoustic feed-back, to produce a strong signal. Obviously when the unit is in the water, gain control 63, mounted on the amplifier, cannot be changed without taking the repeater out of the water. Thus, the surface gain control 92 is used for this purpose and is adjusted to maximum gain before feed-back occurs. From Fig. 7 it is seen that this is accomplished by varying the position of the arm on the gain control, which causes a change in the control voltages applied to the grid of the first tube 50 of the amplifier. 1n the particular model illustrated, excellent gain control over a range of 50 db has been obtained.

Acoustic feed-back is to a large extent eliminated by the arrangement of the hydrophone 18, and projector 29 on the vertical fins 12 and 11. It will be seen from Fig. 8 that the field about the vertical axis of both the hydrophone and projector is substantially uniform. However, as shown in Fig. 9, the field of each about the horizontal axis is variable, increasing to a maximum in the equatorial plane and decreasing to a minimum at the axis. The horizontal field is relatively great as compared to the vertical field and the sensitivity should be confined to approximately from the equatorial plane. This serves to materially eliminate the coupling between the units, which is indicated by the cross-hatched overlapping portions of the fields shown in Fig. 9.

With the device being towed submerged and the switch 45 in its lower position, any sound signal projected from supersonic echo ranging apparatus on one or more vessels which may be intercepted by the hydrophone 18 is amplified and without any appreciable delay is retransmitted out into the water medium at its amplified level. This simulates very accurately the actual echo which would be normally reflected from a very much larger body such as a submarine.

In conclusion while we have specifically described a preferred embodiment of the invention, it will be evident that various changes may occur to those skilled in the art without departing from the spirit and scope of the appended claims.

We claim:

1. A device for use in training personnel in the operation of underwater echo ranging apparatus comprising a body adapted to be submerged in simulation of a submarin the .si'ze or sa d b dyb n elati lysmal a comp r d to said su marine, a hydrophone nd a pr jector each being of the piezoelectric crystal type each having a minimum sensitivity in at least one direction and mounted on said body one above the other on a substantially common axis each in a direction of minimum sensitivity of the other, the sensitivity of said projector and said hydrophone being substantially uniform normal to said mounting axis and substantially greater than the sensitivity along said axis, and an amplifier conneeted between said hydrophone and said projector, whereby any signal projected from said echo ranging apparatus and intercepted by said hydrophone may be amplified and retransmitted by said projector at a higher intensity in simulation of the natural echo which would normaly be Iflected by said submarine.

2. A device for use in training personnel in the operation of underwater supersonic sound echo ranging apparatus comprising a body adapted to be towed under water in Simulation of a submarine, said body including upper and lower vertically extending fins and said body being relatively small as compared to said submarine, a hydrophone mounted in one of; said fins and a projector mounted in the other of said fins, said hydrophone and projector each being of the piezo-electric crystal type and being mounted on a substantially common axis, the axial lengths of said hydrophone and projector and the distance therebetween both being great with respect to the wave length of said sound, and an amplifier connected between said hydrophone and projector, whereby any sound signal projected from said echo ranging apparatus and intercepted by said hydrophone may be amplified and retransmitted by said projector in simulation of the natural echo which would normally be re fiected by said submarine.

3. A sound repeater for use in connection with the operation of supersonic sound underwater echo ranging apparatus comprising a body adapted to be towed underwater by a surface ship, a hydrophone attached to said body for receiving signals from the echo ranging apparatus, an amplifier connected to said hydrophone for amplifying signals therefrom, said amplifier including tuned filter means for emphasizing the frequency of the echo ranging apparatus, and a projector connected to said amplifier for retransmitting signals received by said hydrophone from the echo ranging apparatus substantially simul taneously with its reception, said projector and hydrophone each having a minimum sensitivity in at least one direction and being mounted one above the other on a common axis each in a direction of minimum sensitivity from the other, whereby signals projected by said echo ranging apparatus and intercepted by said hydrophone are amplified and retransmitted by said projector at a higher intensity.

References Cited in the file of this patent UNITED STATES PATENTS 

